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. 2025 May 17;72(1):1–13. doi: 10.1093/cz/zoaf023

Review of the ecological aspects of sympatric species Octopus americanus and Octopus insularis (Cephalopoda: Octopodidae) in the Western Atlantic

Mariana Osório Côrtes 1,✉, Bruna Baleeiro dos Santos 2, Renato Hajenius Aché de Freitas 3,4, C E O’Brien 5, Tatiana Silva Leite 6,7
Editor: Janette Boughman
PMCID: PMC13045820  PMID: 41940272

Abstract

Due to similarities in morphology and overlapping distribution, Octopus americanus and O. insularis (both formerly designated as O. vulgaris) are now considered to be cryptic species inhabiting the western Atlantic, while O. vulgaris inhabits the eastern Atlantic and Mediterranean. The historical lack of distinction made between O. americanus and O. insularis in the scientific literature and fisheries statistics, and persisting confusion regarding the identity and basic biological traits of each species, has hindered proper management of octopus fisheries in the western Atlantic. We attempt to rectify this by identifying the habitat preferences (environmental and biological) of each species from published literature. To this purpose, we compiled 134 studies about O. americanus, O. insularis, and “O. vulgaris” from the western Atlantic and re-identified the species based on the geographic area of occurrence, size, and weight of mature individuals, and visually identifiable morphological and body pattern characteristics. Analysis revealed that O. americanus occurs in temperate waters (15–28 °C), from 0 to 200 m on rocky shores, as well as on sand or shell beds. By contrast, O. insularis occurs from 0 to 50 m in tropical waters with a mean temperature of 23–32 °C, mainly in rocky areas and on coral reefs, and generally targets a greater diversity of prey. The results show that these two species inhabit distinct habitats, which can aid in species identification and in the determination of priority areas for their conservation.

Keywords: conservation, distribution, environmental requirements, habitat, Octopus vulgaris species complex, Octopus fisheries

Graphical Abstract

Graphical Abstract.

For image description, please refer to the figure legend and surrounding text.

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Currently, Octopus vulgaris sensu stricto Cuvier, 1797, known as the “common” octopus, is recognized as inhabiting European and North African Atlantic and Mediterranean coastlines (Amor et al. 2017a; Quinteiro et al. 2020). However, “O. vulgaris” is the nominal target of extensive fisheries operations across continents, including the east coasts of North and South America, the west coasts of Europe and Africa, and the Mediterranean (Sauer et al. 2019). Recent technological advancements, such as underwater photography and genetic sequencing, have revealed that “O. vulgaris” is actually a species complex comprising at least six closely related and morphologically similar species (Amor et al. 2017a). This complex also encompasses O. sinensis d’Orbigny, 1841 from the northwestern Pacific (Gleadall 2016), O. tetricus Gould, 1852 from eastern Australia and New Zealand, O. djinda Amor, 2021 from southwestern Australia (Amor and Hart 2021), O. vulgaris type III from the eastern South Atlantic and Indian Ocean (Amor et al. 2017a), and O. americanus Monfort, 1802 from the western Atlantic (Avendaño et al. 2020a).

In the western Atlantic, O. americanus and O. insularis Leite and Haimovici, 2008 (in Leite et al. 2008a) are cryptic species whose basic biology and ecology are still being disentangled due to centuries of conflation in the scientific literature and in fisheries designations (González-Gómez et al. 2024; Leite et al. 2024). Despite not being a member of the O. vulgaris complex, and having a distinct phylogenetic history (Lima et al. 2020a; Leite et al. 2024), O. insularis has several features in common with O. americanus, including overlapping geographic range (O’Brien et al. 2021), similar sizes (Leite et al. 2008a; Avendaño et al. 2020a) and general body patterns (e.g., deimatic display) and body pattern “components” (e.g., raised papillae) that closely resemble each other. As a result, a number of studies conducted in the western Atlantic have used the name O. vulgaris to refer to both species (e.g., Mather et al. 2012; Hernández-Urcera et al. 2019; Bennice et al. 2021), and, due to a lack of widespread awareness about the updated taxonomy, misidentification persists.

To add to this confusion, Octopus americanus has a convoluted nomenclatural history. It is considered to have been first described based on specimens from the West Indies in 1802 by Montfort D. but was designated as nomen dubium until recently due to inconclusive locality data, a lack of a designated type specimens and insufficient description (Voss and Toll 1998). Based on COI and 16S rRNA analyses, this species was redescribed by Avendaño et al. (2020a) as encompassing western Atlantic “O. vulgaris” and its synonyms distributed from Mar del Plata (Argentina) to Virginia (USA). In the southeastern and southern regions of Brazil, O. americanus is the target of large-scale longline pot fisheries (Ávila-da-Silva et al. 2014) and of commercial “gareteo” (baited line) fisheries in the Gulf of Mexico (Avendaño et al. 2020b). It is also caught as bycatch of the crab Menippe mercenaria trawl fishery in western Florida and of the shrimp trawl fishery in Brazil (Sauer et al. 2019).

By contrast, Leite et al. (2008a) described Octopus insularis as a distinct species based on intensive morphological comparisons between specimens of “O. vulgaris” from Brazilian oceanic islands (Fernando de Noronha archipelago, Rocas Atoll and Sao Pedro and Sao Paulo archipelago), the Northeast region of Brazil, and southern Brazil with O. vulgaris sensu stricto from the Mediterranean (Mangold 1998). Later genetic and body pattern analyses demonstrated that its distribution extends into northern Brazil (Sales et al. 2013), the oceanic islands of Ascension and Saint Helena (Amor et al. 2017b), the Caribbean (Lima et al. 2017; Puentes-Sayo et al. 2021) and the Gulf of Mexico (Flores-Valle et al. 2018; González-Gómez et al. 2018). It also extends as far north as Southern Florida (Maloney et al. 2023), the West Indies and Bermuda (O’Brien et al. 2021) and as far east as São Tomé Island (Lima et al. 2023). This species is closely related to octopuses from the eastern Pacific Ocean such as O. mimus and O. hubbsorum (Lima et al. 2020a). It occurs in tropical reef environments, experiences more rapid growth, and matures at smaller sizes than O. americanus and other species from the O. vulgaris complex (Lima et al. 2014; Batista et al. 2022).

Despite the two species being sympatric, O. americanus and O. insularis exhibit distinct preferences for specific environmental and feeding conditions. In the case of species with ecological and fishing significance, such as O. americanus and O. insularis, it is important to understand their habitat selection and behavioral traits so that they can be better-managed. One way to accomplish this is to synthesize existing information by conducting a comprehensive literature review. Such a review on the ecology and habitat of Enteroctopus dofleini helped resolve specific challenges associated with management of its fishery in British Columbia (Gillespie et al. 1998).

A historical overview of the meaning of “ecological niche” reveals an evolving definition, but with most sources emphasizing the environmental requirements of species (Hutchinson 1978) and the impact of that species on its resources (Elton 1927). Likewise, while a number of interpretations of the word “niche” exist, most agree that two species cannot coexist in a single niche (Gause 1934). If two sympatric species exist in the same environment, they likely differ in their resource consumption and therefore would not be considered to occupy the same ecological niche (Leibold 1995). This is the case for O. americanus and Macrotritopus defilippi (Bennice et al. 2021), as well as O. americanus and O. insularis (Borges et al. 2022; Lima et al. 2023), which, while they often coexist in the same regions and may share the same habitats, certainly do not inhabit the same ecological niche. In this literature review and analysis, we focus on the environmental requirements of each species to determine its preferred habitat. We aimed to: (1) review and synthesize the current scientific literature regarding the ecology of O. americanus and O. insularis in the western Atlantic; (2) differentiate and compare the temperature range, depth range, substrate preference and diet of these species from descriptions available in the literature; and (3) identify any remaining knowledge gaps in the differentiation of these two species.

Materials and methods

This review compiled data from studies of O. americanus and O. insularis in the western Atlantic, Caribbean Sea, Gulf of Mexico, and Florida written prior to 2024. Synonyms of O. americanus and O. insularis, such as Octopus vulgaris type I, type II, Octopus cf vulgaris, and O. vulgaris in association with these geographic regions were used as search terms. Other synonyms, such as Octopus bakerii, O. eudora, O. geryonea, O. tayrona, and O. rugosus, were not used in the search since the scope of our paper was not to perform a taxonomic review on O. americanus and O. insularis, but to clarify ecological differences between them. Scientific papers were found using online databases, such as CAPES, Scopus, Web of Science and Scielo by combining the words “Octopus” AND “americanus” OR “insularis” OR “vulgaris” AND “Brazil” OR “Caribbean” OR “Mexican” AND “Gulf” OR “South” OR “Central” OR “North” OR “Western” AND “Atlantic”, in addition to searching the references of the articles identified. Since there is not much published information about O. americanus’ ecology (only 15 peer-reviewed papers), Brazilian dissertations and theses were also considered, and accessed through the CAPES website (https://catalogodeteses.capes.gov.br/catalogo-teses/). Reviews and technical reports from octopus fisheries were not considered.

Papers were selected based on their titles, abstracts, and keywords. The references were separated and compared according to species, study area, year of publication, academic discipline, and collection methodology. Abiotic parameters (water temperature, depth, substrate type) and biotic parameters (such as diet) were extracted from the text of these references. Laboratory studies in which water temperature and diet were controlled by researchers were not considered in habitat analyses.

Studies of “O. vulgaris” from the western Atlantic were evaluated and the species were reclassified as O. americanus or O. insularis using criteria such as geographic area of occurrence, size, and weight of mature individuals based on Tomás (2003) and Lima et al. (2014), as well as visually identifiable morphological and body patterning characteristics (Leite and Mather 2008; O’Brien et al. 2021) in published photos and/or photos provided by the authors (Table 1, Figure 1). We also created a reliability index to grade our ability to reclassify the species based on the information available in each source. This is outlined in Table 1. Only papers rated as “high” or “moderate” in the quality of information available to identify the species were considered in our analyses (Supplementary Table S1). The information from each source used to reclassify the species was then excluded from subsequent habitat analyses.

Table 1.

Reliability index of the criteria used in species reclassification.

Reliability Species Reclassification Index Criteria Explanation
High Identified from images or videos (Leite and Mather 2008; O’Brien et al. 2021) The species have notable differences in the ventral surface of the arms and in the color around the eyes during the deimatic display, as explained in O’Brien et al. (2021)
Collected from a temperate region (Avendaño et al. 2020a) Distribution range of O. americanus only
Species confirmation from genetic and morphological analyses Genetic markers: COI and 16S rRNA
Moderate Dorsal mantle length (DML) or body weight (BW) of individuals whose reproductive status is known (Tomás 2003; Lima et al. 2014) DML of mature individuals > 190 mm reclassified as O. americanus
DML of mature individuals < 110 mm reclassified as O. insularis
BW of mature individuals < 1520 g reclassified as O. insularis
Low Collected from or observed in a tropical or subtropical region (O’Brien et al. 2021) Distribution range of both species
Size of DML not specified
Absence of images or videos
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Figure 1.

Six images of octopus in the field. The top row shows Octopus americanus inside a den created by the space between rocks (first photo), inside a hole in the sand (second photo) and roaming over sand substrate (third photo). The bottom row shows O. insularis inside a den between rocks (first photo), partially buried in sand (second photo), and over reef substrate (third photo).

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(A), (B) Octopus americanus from Florianópolis, SC, Southern Brazil (A. Thiago Fiuza; B. Athila Bertoncini) and (C) from Rio de Janeiro, RJ, Southeast Brazil (Athila Bertoncini). (D) Octopus insularis from the Turks and Caicos Islands (C.E. O’Brien), from (E) Fernando de Noronha, Northeast Brazil (Tatiana Leite) and (F) from the Bahamas (Melinda Riger).

Geographic range was considered to be a high-reliability reclassification criteria only in temperate regions as an indicator of O. americanus (Table 1). For evaluation of geographic distribution, only areas from which specimens had actually been collected were considered. These areas were divided according to marine ecoregion (e.g., Carolinian, Amazonian, Rio Grande) (Spalding et al. 2007), a smaller scale unit within marine provinces that presents a homogeneous species composition determined by oceanographic and topographic characteristics (e.g., upwelling, temperature, sediment type, currents) and which contain a small number of ecosystem types (Spalding et al. 2007).

The water temperatures at which the species were collected and/or studied in the natural environment were classified into the following categories: < 23 °C, 23.1–25 °C, 25.1–28 °C, and > 28 °C, based on the known range of temperature preferred by these two species (Leite et al. 2008a, 2023). Papers that cited only the water temperature of the region, but without specifying at what temperatures the specimens were found, were not included in these analyses. Depths were separated into a range of categories based on whether specimens were collected via diving (free diving or scuba diving) or fishing. The diving depth categories were: < 2.0 m, 2.1–5 m, 5.1–10.0 m, 10.1–20.0 m, and > 20.0 m. The fishing categories were: < 10 m, 10–20 m, 20.1–50 m, 50.1–100 m, and > 100 m.

Substrate was classified as rocky bottom, reef (biogenic plateaus and live or dead coral reefs), gravel, shell beds, sand, mud, vegetated bottom (sea meadows), and litter (debris of anthropogenic origin), according to the descriptions in each reference. For diet, we identified the three most consumed prey items by the two octopus species and their size ranges (Supplementary Table S2). We also noted the season (accounting for hemisphere)—summer, autumn, winter, and spring—during which spawning and recruitment peak, as well as when each species is most abundant and when mature adults first appear every year.

Statistical analysis

In order to compare the proportions of references for each variable between species, we used the G test (Goodman 1964, 1965; Zar 2010). This test is based on the multinomial probability distribution and can be used to check for differences between proportions of multinomial populations (Goodman 1964) (e.g., the difference between the number of references that record each species as occurring in a particular temperature range) and for differences between proportions of multinomial classes within a population (Goodman 1965) (e.g., the difference between the number of references that record O. americanus as occurring in each temperature category).

Results

A total of 152 studies, including 18 theses and dissertations not published in a peer-reviewed journal, met the literature search criteria for inclusion in this analysis. Of these 152 papers (Supplementary Table S1), 11.8% (N = 18) did not have sufficient information to enable accurate identification or reclassification of the species as O. americanus or O. insularis with moderate to high reliability according to our reliability criteria, and were therefore excluded from analyses. Of the remaining 88.2% (N = 134), 50.7% (N = 68) were classified as being about O. americanus and 60.4% (N = 81) about O. insularis, following our criteria for classification or reclassification.

Chronologically, the first study of O. vulgaris that we determined to be about O. americanus was Kraeuter and Thomas (1975), a taxonomic review of cephalopod fauna off the coast of Georgia (USA) reporting two individual “O. vulgaris” of 116.2 mm ML and 26.4 mm ML caught at a depth of 18–22 m. Since very small O. insularis (< 50.0 mm ML) only inhabit waters up to 5 m deep (Leite et al. 2009a), it is unlikely that an individual of 26.4 mm ML of this species was caught at 18 m deep. This study was followed by 56 other studies about (misidentified) O. americanus from Southeast/South Brazil, the Gulf of Mexico, and the East Coast of the USA, and another 11 articles after the redescription of the species by Avendaño et al. (2020a) (Figure 2A).

Figure 2.

Two graphics. The first one is a column graph displaying the number of studies published about Octopus americanus and O. insularis per two years, from 1972 to 2024. The second graph is a bar graph displaying number of studies published on O. americanus and O. insularis per academic discipline.

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(A) Number of studies published on each species every two years. (B) Number of articles about Octopus americanus and Octopus insularis according to academic discipline. The numbers to the right of the bars indicate the total number of references in each discipline.

The earliest study we determined to be about O. insularis was conducted in the western Atlantic Ocean on “O. vulgaris” by Wodinsky (1972) regarding the timing of the breeding season in Bimini, Bahamas. This study took place on shallow (< 3 m) reefs in the subtropics and we designated this as the first study to be conducted on O. insularis in our dataset based on the fact that octopuses weighing less than 66 g were found year-round and also that spawning adult females weighing less than 466 g were found. In O. americanus, mature females weigh at least 900 g (Tomás 2003). Wodinsky (1972) was followed by 13 studies conducted in the Caribbean, Northeast Brazil, and Bermuda before the official description of O. insularis (Leite et al. 2008a). After that, 56 subsequent studies were published under this name, plus nine studies which referred to it as “O. vulgaris” (Figure 2A).

The ecoregion which is the greatest source of papers on O. americanus is Southeastern Brazil, and for O. insularis it is Northeastern Brazil, including the islands of the Fernando de Noronha Archipelago and Rocas Atoll (Figure 3). Fewer studies have been conducted on O. americanus than on O. insularis in every ecoregion with the exceptions of the Carolinian, Floridian, Amazonian, Southeastern Brazil, and Rio Grande. Most papers on these species were categorized as either “ecological,” “fisheries,” or “taxonomical” (Figure 2B). Notably, while we found no papers on behavior in O. americanus, 21 papers on O. insularis behavior were identified.

Figure 3.

Map showing the number of studies published on Octopus americanus and O. insularis per ecoregion according to Spalding et al. (2007).

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Number of articles about Octopus americanus (blue circles) and Octopus insularis (red circles) by marine ecoregion (Spalding et al. 2007). The map background was downloaded in an open rights image bank and updated with our results on species by Marcus Vinicius dos Santos on the software Adobe Illustrator 2025.

According to the references evaluated, O. americanus is distributed from Connecticut in the USA (41°N) to Chuí (33°S) in southern Brazil, including deep (> 30 m) and cooler regions of the Gulf of Mexico (Figure 3). Though unpublished, the southern-most recorded occurrence of this species is Uruguay (35°S), where it was collected around 50 m during a research expedition (Carranza A., pers. comm.). By contrast, O. insularis occurs only as far south as Rio de Janeiro State (23°S), in Brazil, where there is cold water (20 °C) upwelling from the South Atlantic Central Water (SACW), and as far north as Bermuda (32°N; O’Brien et al. 2021) (Figure 3), which might be facilitated by warm water (> 24 °C) brought north by the Florida Current.

Of the 134 studies reviewed, 76.1% (N = 102) presented environmental data which were used in the description and interpretation of the O. americanus and O. insularis’ ecology. The main findings are highlighted in Table 2. Overall, 27 papers included information on temperature, 80 on collection depth, 47 on substrate type, and 17 on diet. Both species were present on hard and soft substrates, and on marine litter (Figures 1 and 5).

Table 2.

A comparative table of traits (temperature preference, depth range, substrate type, diet and activity period) distinguishing Octopus americanus and Octopus insularis. N = number of references.

Species Octopus americanus Octopus insularis
N e.g. references N e.g. references
Temperature range 13°C–28°C 6 Haimovici and Andriguetto (1986), Castellano et al. (2018) 23°C - 30°C 14 Leite and Mather (2008), Batista et al. (2022)
Average temperature 20°C–23°C 4 Avendaño et al. (2022), Côrtes (2022) 26°C - 28°C 10 Leite et al. (2008a), Batista et al. (2022)
Depth range 0–200 m 24 (fishing samples) Bennice et al. (2021), Araujo and Gasalla (2019) 0–50 m 15 (fishing samples) Leite et al. (2008a)
8 (diving samples) 33 (diving samples)
Substrate type Hard and soft bottom 9 Rosso and Pezzuto (2016), Bennice et al. (2019) Hard bottom 38 Leite et al. (2008a), Dantas et al. (2022)
Diet (prey items) Bivalves > crabs/gastropods 3 Bennice et al. (2021), Côrtes (2022) Crabs, bivalves, gastropods, fish 14 Leite et al. (2016), Urrutia-Olvera et al. (2021)
Main prey* (size range) Larger bivalves (20–119 mm shell width) 3 Bennice et al. (2021), Côrtes (2022) Smaller crabs (7.7–25 mm carapace width) and bivalves (24–30 mm shell width) 14 Leite et al. (2009, 2016)
Activity period nighttime 1 Bennice et al. (2021), personal observations, Côrtes M.O. and Leite T.S. daytime 1 O’Brien et al. (2023)
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*The order of the groups reflects the overall importance found in the studies.

Figure 5.

Pie chart showing the percentage of studies on Octopus americanus and O. insularis per substrate type.

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Number of articles that reported individuals of (A) Octopus americanus and (B) Octopus insularis according to substrate type. Asterisk (*) indicates a significant difference in the number of citations between species per each substrate type (Goodman’s G test, 1964, Gcalc = 3.18).

Octopus americanus was recorded between 13 °C and 28 °C, but mainly at temperatures between 20 °C and 23 °C (67% of references, N = 4). At temperatures below 23 °C, only O. americanus was recorded (Figure 4A). In fisheries samples, O. americanus was most present at depths between 20 and 100 m and, in at least four studies, at depths greater than 100 m (Figure 4B). In dive surveys (N = 8), the majority (87.5%, N = 7) found O. americanus between 2 to 5 m. This species was present in similar proportions on hard (rocky bottom and gravel; 100% of papers, N = 8) and soft substrates (shell beds, sand, mud; 100% of papers, N = 8), and thus may occupy a wider range of environments present in shallow and deep waters than O. insularis (Figure 5). The main prey items of O. americanus reported in the majority studies were bivalves.

Figure 4.

Two graphics. The top one is a column graph showing the number of studies on Octopus americanus and O. insularis per temperature range (below 23 °C, between 23.1 and 25 °C, between 25.1 and 28 °C and above 28 °C). The bottom one is a column graph showing the percentage of studies on O. americanus and O. insularis per depth of collection in fisheries studies only.

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Number of articles (N) by species (Octopus americanus and Octopus insularis, adult individuals only) according to (A) water temperature range (°C) and (B) depth (fisheries samples only). Asterisk (*) indicates a significant difference in the number of citations between species per each temperature or depth category (confidence interval does not include zero for Acritical = 7.43, Goodman’s G test, 1965). Roman numerals and uppercase letter indicate differences between temperature range for Octopus americanus and Octopus insularis, respectively (Gcalc = 2.5, Goodman’s G test, 1964).

Only three papers report the prey of O. americanus. Côrtes (2022) evaluated food remains of juvenile and adult O. americanus in shallow waters up to 15 m in Southern Brazil and found Perna perna (bivalve), followed by Menippe nodifrons (crab) and Semele proficua (bivalve) to be the most abundant species present in prey middens. The size of the crustaceans ranged from 24 to 80 mm (shell length) and 24 to 101 mm (palm length); that of bivalves ranged from 12 to 82 mm (shell length) and 20 to 119 mm (shell width); and that of gastropods ranged from 18 to 56 mm (shell length) and 14 to 38 mm (shell width). Bennice et al. (2021) reported the main prey items consumed by juvenile O. americanus in Florida to be the bivalve Chione elevata, followed by the gastropod Bulla occidentalis and the crustacean Calappa spp., with 0.57 mm being the mean shell thickness of bivalves without a drill hole and 0.74 mm for bivalves with a drill hole. Stable isotope analysis of O. americanus collected in Southern Brazil found that its diet consists of bivalves, gastropods, and crustaceans without differentiating to more specific taxonomic levels (Muto et al. 2014).

Three studies demonstrated that the highest abundance of mature O. americanus occurs during autumn and winter in shallow areas (up to 30 m) of subtropical regions and during spring and summer at greater depths. However, while the abundance of mature individuals peaks at those times, mature individuals were observed throughout the year in the subtropics, both in shallow and deep water, in both hemispheres. At higher latitudes in both hemispheres, spawning females have been recorded throughout the year, but O. americanus spawning in shallow water (up to 30 m) has mainly been recorded during spring, followed by a peak in paralarvae abundance during late spring and early summer, and then a peak in juveniles during spring (March to May in the Northern hemisphere and October and November in the Southern hemisphere), summer (June to August in the Northern hemisphere and December to February in the Southern hemisphere) and early fall (March to May in the Southern hemisphere).

In contrast to O. americanus, O. insularis was recorded at temperatures of 23 °C to 32 °C, with 80% of the studies (N = 16) recording a mean temperature between 26 °C and 28 °C. There were significantly more references to O. insularis at 25 °C to 28 °C (N = 14) than at other temperatures (confidence interval does not include zero for Acritical = 7.43, Figure 4A). Octopus insularis inhabits shallower waters than O. americanus, as it was collected mostly on dive and fishing surveys conducted at less than 20 m (N = 46 surveys) (Figure 4B) and was never recorded at depths greater than 100 m. Octopus insularis was predominantly found on hard substrates (rocky bottom, reef, gravel) in all studies of this species (N = 38). The substrate types on which O. insularis was found most were reef beds (65.8% of studies—N = 25), rock (55.3%, N = 21) and gravel (28.9%, N = 11). These values were significantly greater than occurrence on shells beds, mud, vegetated bottom, and litter (13.2%, N = 5) (confidence interval does not include zero for Acritical = 10.78) (Figure 5). Papers that mentioned the presence of O. insularis on sand concerned instances in which individuals were found on sandy patches between rocks or coral reefs, and never on an open sandy plain, in contrast to O. americanus (Figure 5). In addition, no study reported O. insularis dens in soft substrate, although it can partially bury and camouflage in the sand (Figure 1B), in contrast to O. americanus, which can make a hole in gravel or coarse sand (Figure 1E).

The main prey items of O. insularis reported were crustaceans. All 14 papers on the diet of O. insularis mentioned the species of prey consumed (Supplementary Table S2). The items most consumed by juvenile O. insularis were crustaceans and bivalves, mainly crabs of the genus Mithrax and bivalves of the genera Chlamys and Lima. Adults consumed crustaceans (mainly crabs of the genera Mithraculus and Mithrax), gastropods (mainly Lithopoma olfersii), and bivalves (mainly Anadara notabilis). The size of crustacean carapaces consumed by juveniles ranged from 4 to 34 mm and the length of the chela ranged from 18 to 27.5 mm. The width of crustacean carapaces consumed by adults ranged from 7.7 to 25 mm. The shell width of bivalves consumed by adult O. insularis ranged from 24 to 30 mm and that of gastropods from 25 to 45 mm.

Mature O. insularis have been recorded year-round in shallow waters (up to 40 m), both in Northeast Brazil and the Gulf of Mexico, suggesting that this species may reproduce throughout the year in these regions. However, more adults are observed in winter and spring (from December to May in the Northern hemisphere and from July to December in the Southern hemisphere), when the spawning peak occurs, and a peak in the abundance of juveniles is observed in the summer (during July in the Northern hemisphere and December to February in the Southern hemisphere) when the average water temperature is highest (> 27 °C).

Discussion

We conducted a systematic review of the literature on O. americanus, O. insularis and “O. vulgaris” in the western Atlantic, reclassifying the papers about “O. vulgaris” as either O. americanus or O. insularis based on their geographic distribution, maturation size and body patterns, and grading the reliability of the information available for reclassification. Based on this review, we were able to provide habitat descriptions (e.g., temperature and depth range, substrate type, and diet) of the two species from 134 studies conducted since 1972.

The bibliographic search method used in this study enabled us to collate and summarize the broad scope of existing knowledge about the ecology of O. americanus and O. insularis, although this method may have inadvertently excluded some relevant references, particularly theses and dissertations from Central American universities as well as literature from prior to 1970 and references from synonyms other than “O. vulgaris.” For example, Robson (1929) and Pickford (1946) acknowledge some specimens from Western Atlantic identified as Octopus rugosus that could either be O. americanus or O. insularis, based on the specimen’s morphological description provided and areas of co-occurrence. The fewer references on O. americanus in comparison to O. insularis likely reflects the relative shallowness and accessibility of tropical reefs, where O. insularis is more abundant. Additionally, a recent study found that O. insularis is diurnal in its natural environment (O’Brien et al. 2023), while field studies carried out in Brazil and in Florida showed that O. americanus is nocturnal (Côrtes M.O. and Leite T.S., pers. comm., Bennice et al. 2021) following the Octopus vulgaris s.s. pattern (Kayes 1974).

Our analysis highlights the differences in the habitats of O. americanus and O. insularis respectively. In tropical regions, where the two species co-occur, each occurs at different water temperatures and depths: O. americanus occurs in deeper (> 30 m), cooler (15–25 °C) waters while O. insularis occurs in shallower (< 30 m), warmer (23–32 °C) areas (Avendaño et al. 2020b, 2022; Puentes-Sayo et al. 2021). Our results indicate that in subtropical regions with water temperatures between 23 °C and 25 °C, both species occur, such as South Florida. In these areas of overlap, other ecological factors, such as substrate type, dictate their respective location. Understanding these differences could aid in field identification of species, particularly in water temperatures below 23 °C or above 25 °C, and help identify new areas of occurrence for these species, which may expand their latitudinal distribution in response to global climate change, as predicted by species distribution models (Lima et al. 2020b; Borges et al. 2022). One might speculate that as sea water temperature rises, O. americanus would migrate to higher latitudes or deeper waters, associating with a wide variety of substrates (Borges et al. 2022). Likewise, O. insularis, being the most abundant and dominant octopus species in the shallow tropical waters of the western Atlantic, which is typically found on hard substrates as coral reefs, may expand its distribution range to higher latitudes as surface water temperatures increase (Leite et al. 2024). However, it is unlikely to move into deeper waters, as it is primarily associated with hard substrates.

In addition to depth range and temperature, each species has different substrate preferences. O. americanus inhabits a wider variety of substrate types in shallow (< 30 m) to deep (200 m) waters, including rocky shores, sandy bottoms, gravel, and shell beds. This is similar to other members of the O. vulgaris species complex, such as O. vulgaris s.s. and O. tetricus, which have also been observed in dens on rocky bottoms, sandy bottoms and shell beds (Katsanevakis and Verriopoulos 2004; Godfrey-Smith and Lawrence 2012; Guerra et al. 2014; Garci et al. 2016). By contrast, O. insularis inhabits mainly hard substrates, such as reef environments, limestone rock and live or dead coral, characteristic of shallow waters in tropical regions. It therefore appears that species in the O. vulgaris complex are characterized by their ability to make their dens on both soft and hard substrates, while O. insularis only uses hard substrates. This difference can aid in correctly identifying species in the field, especially where they co-occur geographically and thermally.

Food availability can also influence the distribution of octopuses and be important in defining the ecological niche of a species (Vincent et al. 1998; Guerra et al. 2014). Although both species feed on bivalves, gastropods and crustaceans (Anderson et al. 2008; Bennice et al. 2021) and have a wide and varied diet, records indicate that O. americanus has a greater preference for large bivalves (Bennice et al. 2021; Côrtes 2022), while O. insularis preys mainly on crustaceans and small bivalves (Leite et al. 2009b, 2016). This suggests differences in the two species’ feeding strategies, although only a few studies have been conducted on the diet of O. americanus, and thus more research is needed in order to establish this definitively. It is likely that O. americanus feeds mainly on bivalves due to their higher availability, as is suggested for some populations of the O. vulgaris species complex (Smale and Buchan 1981; Ambrose and Nelson 1983; Guerra et al. 2014). The preference for more abundant and available organisms in the environment is related to a lower variety of prey in the diet, as shown by the fact that only three species accounted for more than 57% and 70% of O. americanus’ food remains (Bennice et al. 2021; Côrtes 2022, respectively). On the other hand, most studies on O. insularis showing preference for a greater diversity of prey may be due to a wide variety of species in tropical reefs and its “time-minimizing” hunting strategy that incentivizes gathering as much as food as possible during short daytime hunting trips to minimize exposure to predators (Mather and O’Dor 1991; Leite et al. 2009b; O’Brien et al. 2023). However, since an octopus can change its hunting tactics and foraging behavior over time (Leite et al. 2009b) defining feeding behavior is complex.

Differences in prey may also reflect the respective habitat preferences of each species, since bivalves can more easily be found buried in sandy and muddy bottoms than crustaceans, which are more commonly found on rocky bottoms or reefs (Melo 1996; Gosling 2003). Since food availability affects octopus distribution, the food preference of each species may determine their respective occurrence within regions of overlap. Understanding preferred feeding areas will help in planning the establishment of any future protected areas targeted at these species (Guerra et al. 2014).

Although both species were sampled through longline pot fisheries, O. americanus was primarily sampled in industrial fisheries and trawl fisheries, which occur at depths > 50 m (Haimovici and Andriguetto 1986; Perez and Pezzuto 1998). By contrast, most studies of O. insularis were conducted via snorkeling or scuba diving in shallow water (e.g., Mather 1991; Urrutia-Olvera et al. 2021), or by longline from artisanal and commercial pot fisheries in Northeastern Brazil, which occur in shallower areas up to 40 m (Braga et al. 2007; Batista et al. 2022), or through free diving and “polvejamento” (fishermen that walk over the reef during low tide and catch octopus using hooks). This difference in catch methods emphasizes the different depth preferences of each species and also implies that the two species should have different management plans, in contrast to existing legislation which lumps both together (Sauer et al. 2019). Additionally, fisheries managers should consider how each type of fishery targeting the species may influence their conservation status. Given that O. insularis is the target of artisanal fisheries and is better-studied in terms of its fisheries and management (e.g., Leite et al. 2008b; Andrade 2016; Flores-Valle et al. 2018), it is likely that its population is better-protected than O. americanus. The latter has had fewer studies of its behavior and preferred distribution areas, and is likely more-intensely exploited, making its unknown conservation status particularly concerning. Misidentification and the lack of ecological information about O. americanus can contribute to unsustainable exploitation of the species.

It is recommended that fisheries managers commence independent regulation of each species according to its habitat preferences, and to differentiate between them in catch statistics, in order to better understand if populations are at risk or not. Knowing the preferred habitat traits would enable conservationists to propose and delimit sensitive areas for each species. Added to that, only a few countries (Brazil, Mexico, and Venezuela) currently have octopus fisheries legislation, and only Brazilian and Mexican regulations differentiate between these two species. Proper regulation requires not only differentiation between the two but also a better understanding of where each species reproduces, matures, and feeds, and when it spawns. Thus, we recommend that octopus fishery regulations in Brazil, Mexico and Venezuela be updated with information on the habits of each species. In those places where both species occur and are the target of fisheries, a better understanding and differentiation of species will permit setting separate catch quotas, which may help prevent overexploitation on one or other species if its population is smaller than initially thought, especially considering both species have different maturation sizes. If so, a reduction in allowable commercial catches could avert their overexploitation. For O. americanus, we recommend that commercial fishing be excluded from rocky shores in cool, shallow waters of subtropical regions, which are important areas for recruitment and feeding (Côrtes 2022; Haimovici et al. 2024), and that artisanal fishing be discouraged during the late summer and early autumn months, when there are more juveniles and subadults in shallow areas (Côrtes 2022). For O. insularis, it is important to regulate illegal fishing in waters up to 2 m deep in tropical regions, which are nursery habitat for juveniles (Leite et al. 2009a, 2024).

It is somewhat perplexing and worrisome that O. americanus, one of the most abundant octopus species in the western Atlantic and the target of many large-scale fisheries, has had so few studies conducted on its ecology and behavior, and that no information about its species-specific habits have been incorporated into its management plans. Thus, there is an urgent need for more research on O. americanus and to update fisheries management plans according to the habitat characteristics of both O. americanus and O. insularis.

Conclusion and recommendations

Despite the coexistence of this sympatric species, our review identified important differences in habitat preferences and niche between O. americanus and O. insularis. Water depth and temperature are two traits that can be used to reliably differentiate between the two species, with the former generally inhabiting deeper, cooler waters than the latter. Distinguishing and understanding the preferred habitats of these species is critical given that both were regularly misidentified as O. vulgaris (Sauer et al. 2019) and are important fisheries resources in the western Atlantic.

Since it was not possible to distinguish between species in 18 of the references initially identified, held in locations where both species occur, such as Gulf of Mexico, Venezuela, and Ceará state in Northern Brazil, we recommend that future studies in those areas report ecological data gathered during sampling, and that researchers include morphological and genetic analyses to assure correct identification of species (e.g., Avendaño et al. 2025). This is especially important considering that both species are fisheries targets in those regions.

This study aimed to create ecological profiles of O. americanus and O. insularis that could aid in field identification of the two species. It is not a substitute for morphological and genetical analyses, but a more accessible, no cost, and minimally invasive complement. We encourage future studies to utilize these criteria in making their species identifications and to include pictures or videos of their specimens as Supplementary Material.

Currently, there is a decent understanding of the behavior and population dynamics of O. insularis, but relatively few studies on these topics in O. americanus. Understanding the recruitment, reproduction, spawning, feeding areas, and seasonality of this species is essential for its management, especially since it is a fisheries target (Caputi et al. 2014; Lima et al. 2017). Further field studies of O. americanus’ ecology, distribution, habitat use, population structure, and reproduction are therefore encouraged.

Supplementary Material

zoaf023_suppl_Supplementary_Table_S1
zoaf023_suppl_supplementary_table_s1.pdf (249.3KB, pdf)
zoaf023_suppl_Supplementary_Table_S2
zoaf023_suppl_supplementary_table_s2.pdf (77.6KB, pdf)
zoaf023_suppl_Supplementary_Table_S3
zoaf023_suppl_supplementary_table_s3.pdf (40.4KB, pdf)

Acknowledgments

The present work was part of Mariana O. Côrtes’ Master’s thesis. We thank Dr. Manuel Haimovici, Dra. Bárbara Segal, Dr. José Angel Perez, and Dra. Andrea Freire for their constructive comments on an early version of this paper and anonymous reviewers from Sci. Mar. for comments on a more updated version of this paper. We also thank the anonymous reviewers from Current Zoology for helping improve this article. We extend our thanks to Marcus Vinicius dos Santos for illustrating the map in Figure 3 and Dr. Alvar Carranza, professor at Universidad de la República de Uruguay, for information about O. americanus in Uruguay.

Contributor Information

Mariana Osório Côrtes, Programa de Pós-Graduação em Ecologia, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina 88037-000, Florianópolis, Santa Catarina, Brasil.

Bruna Baleeiro dos Santos, Laboratório de Métodos de Estudos Subaquáticos e Cefalópodes (LAMECE), Centro de Ciências Biológicas, Universidade Federal de Santa Catarina 88037-000, Florianópolis, Santa Catarina, Brasil.

Renato Hajenius Aché de Freitas, Programa de Pós-Graduação em Ecologia, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina 88037-000, Florianópolis, Santa Catarina, Brasil; Laboratório de Biologia de Teleósteos e Elasmobrânquios (LABITEL), Centro de Ciências Biológicas, Universidade Federal de Santa Catarina 88037-000, Florianópolis, Santa Catarina, Brasil.

C E O’Brien, Center for Marine Resource Studies, The School for Field Studies, 1, Cockburn Harbour TKCA 1ZZ, Turks and Caicos Islands.

Tatiana Silva Leite, Programa de Pós-Graduação em Ecologia, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina 88037-000, Florianópolis, Santa Catarina, Brasil; Laboratório de Métodos de Estudos Subaquáticos e Cefalópodes (LAMECE), Centro de Ciências Biológicas, Universidade Federal de Santa Catarina 88037-000, Florianópolis, Santa Catarina, Brasil.

Supplementary material

Supplementary material can be found at https://academic.oup.com/cz.

Funding

We gratefully acknowledge the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for granting Mariana O. Côrtes a MSc scholarship and Fundo Brasileiro para a Biodiversidade (FUNBIO, nº 007/2021) and Instituto Humanize for the financial support granted to Mariana O. Côrtes through the Programa Bolsas FUNBIO Conservando o Futuro.

Ethics statement

The study was not submitted to an ethics committee since it was a bibliographic search and review. The authorship of all images and information not provided by the authors is acknowledged.

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zoaf023_suppl_Supplementary_Table_S1
zoaf023_suppl_supplementary_table_s1.pdf (249.3KB, pdf)
zoaf023_suppl_Supplementary_Table_S2
zoaf023_suppl_supplementary_table_s2.pdf (77.6KB, pdf)
zoaf023_suppl_Supplementary_Table_S3
zoaf023_suppl_supplementary_table_s3.pdf (40.4KB, pdf)

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